A reserve battery is a primary or secondary battery in which part is isolated until the battery needs to be used. When a long storage period is required, reserve batteries are often used, since the active chemicals of the cell are segregated or exist in an inactive state until needed, thereby reducing self-discharge. Common types of reserve batteries include aluminum batteries, silver-zinc batteries, thermal batteries, and water-activated batteries.
Liquid reserve batteries typically require a substantial activation time due to the time required for the electrolyte to penetrate and effectively contact the electrodes, even when the electrolyte is introduced into the battery under pressure.